I'm working on building my own long travel suspension, and while I'm at it I'd like to dial in the geometry a little better while I have the chance. So my question is about Anti-Dive. I notice that pretty much all of the "Go-Fast" vehicles have 0% Anti-Dive. Even most of the Ultra4 IFS buggies have 0% Anti-Dive it looks like. Looking at Jorgan Pellegrino's IFS/IRS U4 car has negative Anti-Dive %(Pro-Dive?). Then I look at the solid axle/rock crawler guys and some of them are running 50%-200% anti-dive. I know solid axle is a whom other animal but I figured I'd throw that out there for comparison sake. Sounds like having parallel arms is the way to go. It helps avoid bump steer since the caster doesn't change throughout the suspension cycle and you don't have to worry about caster curve. I'm just wondering how it will handle on the street compared to having some anti-dive built in? I don't plan on a lot of street driving but I do plan on driving on the street to get to trails sometimes. It'll mostly be on a trailer these days though. I hear you can mitigate the "Dive" by tuning your spring rates and bypasses to help reduce the dive in the front end. I just don't know exactly what is needed to be done. Just higher spring rates and stiffer low speed valving?
Something to point out as well. There are two separate forces that effect front end dive. Both can be tuned by the suspension geometry and are related to each other. The first one is the one you can see by playing with the basic suspension calculators. (Triaged 3 and 4 link calculators will show this form of anti-dive/anti-squat). This anti-dive is the exact opposite of anti-squat. The forces are just applied in the opposite direction since it's on the front end of the vehicle and happens during deceleration. This is effected by the suspension geometry and its relation to the COG (Center of Gravity). This is inertia induced anti-dive.
The second one seems to be a more important one based on my readings, but it's harder to calculate without expensive software. It can be brought to a neutral position easily by having 0% anti-dive (parallel links/arms from side view and level with the ground.) On IFS cars, this anti-dive or lack thereof can be constant throughout suspension cycle since the arms stay parallel and level with the ground (when viewed from the side). On solid axle vehicles this number will change throughout suspension cycle since the arms change angle as the suspension cycles. The way this Anti-Dive works is when you apply the brakes, the spindle will want to rotate forward. If there is anti-dive (picture upper arm slanted back, sloping down towards the back). As the spindle wants to rotate as the brake force is applied, the rotation of the spindle will want to pull the upper arm down and forward. This causes the suspension to want to push down/lift the chassis up. This force is known as anti-dive. It is torque induced instead of inertia induced liked I mentioned above. This seems to have a greater effect on suspension than the inertia induced anti-dive. Having the links or arms parallel and level with the ground gives a 0% Anti-Dive in both forms.
Here is a link to a good thread on this stuff. Where I got a lot of my information on this. - http://www.4x4-16.com/Basic-IFS-IRS-anti-squat-dive-tech-with-a-twist_10823326-2.html
There are some really good illistrations in that thread too. I will pull some over here when I get some more time.
Something to point out as well. There are two separate forces that effect front end dive. Both can be tuned by the suspension geometry and are related to each other. The first one is the one you can see by playing with the basic suspension calculators. (Triaged 3 and 4 link calculators will show this form of anti-dive/anti-squat). This anti-dive is the exact opposite of anti-squat. The forces are just applied in the opposite direction since it's on the front end of the vehicle and happens during deceleration. This is effected by the suspension geometry and its relation to the COG (Center of Gravity). This is inertia induced anti-dive.
The second one seems to be a more important one based on my readings, but it's harder to calculate without expensive software. It can be brought to a neutral position easily by having 0% anti-dive (parallel links/arms from side view and level with the ground.) On IFS cars, this anti-dive or lack thereof can be constant throughout suspension cycle since the arms stay parallel and level with the ground (when viewed from the side). On solid axle vehicles this number will change throughout suspension cycle since the arms change angle as the suspension cycles. The way this Anti-Dive works is when you apply the brakes, the spindle will want to rotate forward. If there is anti-dive (picture upper arm slanted back, sloping down towards the back). As the spindle wants to rotate as the brake force is applied, the rotation of the spindle will want to pull the upper arm down and forward. This causes the suspension to want to push down/lift the chassis up. This force is known as anti-dive. It is torque induced instead of inertia induced liked I mentioned above. This seems to have a greater effect on suspension than the inertia induced anti-dive. Having the links or arms parallel and level with the ground gives a 0% Anti-Dive in both forms.
Here is a link to a good thread on this stuff. Where I got a lot of my information on this. - http://www.4x4-16.com/Basic-IFS-IRS-anti-squat-dive-tech-with-a-twist_10823326-2.html
There are some really good illistrations in that thread too. I will pull some over here when I get some more time.